Setting multiple gravity
Fact that a tank reachs a ground faster than a feather falling from the same high is not a question of gravity, but matter of air friction. Thanks Lemon for pointing out :)

v01 Force Field - Drag
You can set Rigid Body as usual...

add Cube - enable Rigid Body simulation &gt; Mass &gt; 100 kg
add Plane - enable Rigid Body simulation &gt; Mass &gt; 0,6 kg

and simulate Air friction by adding Force field object (like Drag type) and play with Strength value. Here Linear 0.01


Notes
Example above is option how to slowdown falling object based on mass, without any physical accuracy, just to get desired effect.
For some reason speed fall is affected also by Dynamics &gt; Damping Translation. Two objects, both of mass 1 kg, but one object with damping increased to 0.8 also gives air friction effect.

v02 Cloth Sim
Another option is to use cloth simulation, that has a parametr Air Viscosity per object, so it can be adjust individually.

In this example also Cube use Cloth sim, that with some setting can react as solid object. For tank you can just use Rigid Body as before.